It is known to use antifreeze compositions in heat exchanging systems and/or for de-icing applications. In these applications, the antifreeze compositions come in contact with various metals, alloys, and other components forming the different parts of the heat exchanging system or the system to be de-iced. Efforts have been made towards the protection from corrosion of parts and components in contact with the antifreeze compositions. Prior art solutions include the addition of various corrosion inhibitors and/or the use of different organic acids for multiple metal protection systems.
Corrosion protection is critical at all temperature ranges. However, at low temperatures, other factors important to the performance of antifreeze compositions come into play, including the unwanted formation of scale and/or deposits. Water is often used to dilute antifreeze compositions. Water quality varies greatly with geographic location, population and degree of industrialization. When hard water is used, scales can be formed from alkaline earth metal carbonate and phosphate deposition. These inorganic films tend to inhibit thermal transfer and thus reduce the heat transfer efficiency of the system. Besides the use of hard water, the use of certain corrosion such as molybdates inhibitors contribute to the formation of deposits, e.g., silicate gellation. In certain additive packages for coolants, silicate/phosphate corrosion inhibitors are used to help protect metal cooling system parts and also as a buffer to control the pH of the antifreeze. When a composition containing silicates/phosphates is mixed with hard water, copious precipitates develop in a short period of time. These precipitates may clog a cooling system, resulting in reduced antifreeze/coolant flow, increased engine operating temperatures and shorter service life. Deposit formation can also result in the physical damage of soft material parts, e.g., water pump seals, engine head seals, hoses, etc. used in the parts and components of the system.
To alleviate the silicate deposit problem, silicate stabilizers can be added to antifreeze compositions. However, at low operating temperatures, e.g., sub-freezing, some additives are not soluble thus further compounding the problem. Ideally, antifreeze compositions should remain transparent and free of insoluble materials in operation as the unwanted formation of deposits/soluble materials decreases the heat transfer property of the composition.
There is still a need for an antifreeze composition, i.e., a glycol based composition, having improved thermal stability at low temperatures with minimal salt/deposition formation. A molybdate-free antifreeze compositions possesses the required characteristics.